In a steam turbine, pressure and temperature energy of high-temperature and high-pressure steam supplied from a boiler is converted into rotational energy by using a blade cascade combining stator blades and rotor blades. FIG. 2 illustrates a conceptual view of a power generation system using the steam turbine as stated above.
As illustrated in FIG. 2, steam generated at a boiler 1 is further heated at a heater 2, and guided to a steam turbine 3.
The steam turbine 3 is made up by arranging stages made up of a combination of a rotor blade implanted in a circumferential direction of a turbine rotor 4 and a stator blade supported by a casing in an axial direction of the turbine rotor 4 in plural stages. The steam guided to the steam turbine 3 expands inside a steam passage, and thereby, the high-temperature and high-pressure energy is converted into the rotational energy by the turbine rotor 4.
The rotational energy of the turbine rotor 4 is transmitted to a power generator 9 connected to the turbine rotor 4, and converted into electric energy. On the other hand, the steam losing the energy thereof is discharged from the steam turbine 3 and guided to a steam condenser 10. Here, the steam is cooled by a cooling medium 11 such as seawater, and condensed to be condensed water. This condensed water is supplied to the boiler 1 again by a feed pump 12.
The steam turbine 3 is made up by being divided into a high pressure turbine, an intermediate pressure turbine, a low pressure turbine, and so on depending on a condition of a temperature, a pressure of the supplied steam. In the power generation system as stated above, oxidation of parts of the rotor blades, the stator blades and so on of the steam turbine is remarkable because the parts are exposed to the high-temperature steam especially at the stages of the high pressure turbine and the intermediate pressure turbine.
Surface roughness of the rotor blade, the stator blade and so on of the steam turbine is reduced as much as possible by a method in which fine particles are sprayed on surfaces thereof or the like when they are incorporated as the parts. This is because a flow of fluid gets out of order at the surface of the blade and so on when the surface roughness of the parts is large, aerodynamic characteristics as a blade deteriorate resulting from separation, and this may cause deterioration of efficiency of the whole turbine.
These parts represent high aerodynamic performance in an initial state because the surface roughness is reduced when they are used in an actual plant. However, the surface roughness of these parts gradually becomes large as the oxidation of the surface of the parts proceeds, and the aerodynamic performance of the blade gradually deteriorates as an operation time passes. Accordingly, there is a problem that the efficiency of the turbine as a whole also deteriorates. Proposals as stated below have been made as arts relating to a surface treatment of the steam turbine parts.
A method is proposed in which a nitrided hard layer (radical nitrided layer) is formed and thereafter, a physical vapor deposition hard layer such as CrN, TiN, AlCrN is further formed thereon to improve an erosion resistance, an oxidation resistance, and a fatigue strength of the steam turbine parts and so on (for example, refer to JP-A 2006-037212 (KOKAI)).
Besides, a method is proposed in which a corrosion resistance and a high-temperature erosion resistance of the blade are improved by forming a layer composed of iron boride and nickel boride at the blade surface by performing a boride treatment by immersion after a nickel plating is performed, for a member for high temperature of the steam turbine blade and so on (for example, refer to JP-A 2002-038281 (KOKAI)).
A method is proposed in which the corrosion resistance, an abrasion resistance, and the erosion resistance are improved by forming a layer of Cr23C6 by a combination of a thermal spraying and a heat treatment for the steam turbine blade and so on (for example, refer to JP-A 08-074024 (KOKAI), JP-A 08-074025 (KOKAI)).
Besides, a method is proposed in which a corrosion resistance is improved by so-called a laser plating in which the cobalt based alloy of which composition is rigidly controlled is disposed to contact a base material, and thereafter, it is melted and adhered by using a laser for the steam turbine blade (for example, refer to JP-A 2004-169176 (KOKAI)).
A method is proposed in which erosion for solid particles is reduced by forming carbide ceramics (Cr3C2) by high temperature and high pressure gas flame spraying for the steam turbine blade (for example, refer to JP-A 2004-232499 (KOKAI)).
However, improvement in durability of blades is an object of all proposals, and they are not studied from points of views of a surface roughness change caused by oxidation and deterioration of aerodynamic characteristics of the blade in accordance with the surface roughness change. Accordingly, there has not been a proposal to perform the surface treatment from the point of view of the surface roughness change caused by the oxidation and the deterioration of the aerodynamic characteristics of the blade in accordance with the surface roughness change.
The present invention is made to correspond to the conventional circumstances, and an object thereof is to provide a steam turbine and a steam turbine blade capable of suppressing the surface roughness change of the steam turbine blade caused by the oxidation and the deterioration of the aerodynamic characteristics of the steam turbine blade in accordance with the surface roughness change, and maintaining an initial high turbine efficiency level for a long time.
The present inventors devote themselves to study relating to a steam turbine blade structure to maintain a turbine performance. As a result, the present invention is completed by finding out that it is possible to suppress the deterioration of the aerodynamic characteristics of the steam turbine blade by suppressing the surface roughness change caused by the oxidation, and to maintain the turbine performance at a high level for a long time by maintaining the initial high aerodynamic characteristics for the steam turbine blade.
Namely, an aspect of the steam turbine of the present invention includes: a turbine rotor; a rotor blade implanted to the turbine rotor; a stator blade provided at an upstream side of the rotor blade; and a turbine casing supporting the stator blade and including the turbine rotor, the rotor blade and the stator blade, in which a stage is formed by a pair of the rotor blade and the stator blade, and a steam passage is formed by arranging plural stages in an axial direction of the turbine rotor, and in which a surface treatment suppressing an increase of a surface roughness caused by oxidation is performed for at least a part of a surface of the stator blade and a surface of the rotor blade.
Besides, an aspect of a steam turbine blade of the present invention, used for a steam turbine including: a turbine rotor; a rotor blade implanted to the turbine rotor; a stator blade provided at an upstream side of the rotor blade; and a turbine casing supporting the stator blade and including the turbine rotor, the rotor blade and the stator blade, in which a stage is formed by a pair of the rotor blade and the stator blade, and a steam passage is formed by arranging plural stages in an axial direction of the turbine rotor, as the stator blade or the rotor blade, in which a surface treatment suppressing an increase of a surface roughness caused by oxidation is performed for at least a part of surfaces thereof.